So far, polyester coatings are used in many cases for outdoor coating of roofs and walls, especially for coating of a metal plate called pre-coat metal (PCM) which is processed after the coating. This is because polyester coatings are excellent in processability, transparency, curability and coloring property.
However, recently as environmental changes such as air pollution advance, a lot of oil droplets and dusts have come to be contained in the air, and as a result, there are problems that coating films on building materials and automobiles are easily stained more than before and such stains are difficult to remove.
Accordingly, coating films formed are demanded to have property of inhibiting deposition of outdoor stains for a long period of time from an initial stage of coating.
For improving such property of inhibiting deposition of stains, there have been developed techniques of blending a silane compound to a coating composition to make a coating film surface hydrophilic, thus making hydrophobic stains to be hardly deposited, and further removing deposited stains with flowing raindrop or the like (WO 94/06870, JP4-275379A, U.S. Pat. No. 6,486,239 and JP7-82520A).
However, a degree of hydrophilization of a coating film surface and repeatability thereof are still insufficient, long-term property of inhibiting deposition of stains is not always secured, and a large amount of silane compound is required for making a coating film surface hydrophilic. As a result, coatings are not satisfactory from the viewpoint of curability, compatibility, re-coatability, storage stability, a life (pot life) from mixing to coating, anti-floating property, defoaming property, workability in coating and processability of a coating film.
Also, there are known techniques of using an additive prepared by modifying a silicate compound with fluorine for the purpose of exhibiting hydrophilic property from an initial stage of coating (WO 96/26254, JP2001-151970A and JP11-333992A).
However, any of the mentioned techniques are not satisfactory from the viewpoint of re-coatability, storage stability, pot life, defoaming property, workability in coating and processability of a coating film. Especially, hydrophilic property and property of inhibiting deposition of stain of an obtained coating film are greatly lowered because a pot life is short and hydrolysis occurs in the coating composition before coating and gelling starts due to condensation unless coating is initiated soon after blending of a coating.